Effect of Ti,Zr and Mg addition on inclusions and the impact toughness of heat affected zone in low carbon steel

In order to understand the effects of titanium,zirconium and magnesium on inclusions and the impact toughness of heat affected zone（HAZ） of steel,four low carbon steels deoxidized by titanium,zirconium and magnesium were obtained.After melting,forging,rolling and welding simulation,the inclusion characteristics （size,distribution,morphology and chemistry） analysis,Charpy-type test and the fracture observation of the specimens after the Charpy-type test were carried out respectively.The following results were found.A linear relationship exists between inclusions density and Ti content when Ti content ranges from 0.004%to 0.032% without Mg,and the proportion of inclusions in diameter less than 0.5μm decreases with the increasing of Ti content in steel.The density of inclusion increases rapidly when adding Ti-Zr-Mg deoxidant.The addition of Ti-Zr-Mg can enhance the impact toughness of HAZ after welding simulation.The maximal impacting energy after welding simulation is 249 J at 253 K.The complex particles of MgO-ZrO;-TiO;-MnS are most benefit to enhance impact toughness.